1. Field of the Invention
The present invention relates to a liquid crystal display apparatus, and more particularly to a liquid crystal display apparatus of IPS (In-Plane Switching) system in which liquid crystal is made to drive within a surface approximately parallel to a TFT (Thin Film Transistor) substrate by applying a voltage to a pixel electrode and a common electrode therebetween formed on the TFT substrate.
2. Description of the Related Art
An active matrix type liquid crystal display apparatus, having a picture quality of high dignity, uses a thin film transistor (hereinafter referred to TFT) as a switching element of pixels, and is widely used as space-saving designed monitor of a desktop computer and so forth. Generally, in the operating mode of the liquid crystal display apparatus, there are two systems of Twisted Nematic: TN system which allows direction of directors of oriented liquid crystal molecules to be rotated in the perpendicular direction to a transparent substrate and In-Plane Switching: IPS system which allows liquid crystal molecules to be rotated in the direction parallel to a transparent substrate.
The IPS system liquid crystal display apparatus alternately forms pixel electrode and common electrode on the first transparent substrate constituting the TFT, wherein the teeth of a comb of the pixel electrode is parallel to the teeth of a comb of the common electrode with each other, and a light transmission quantity is controlled by changing the direction of the director of the liquid crystal molecule with forming electric field parallel to the substrate by applying a voltage to the pixel electrodes and the common electrodes therebetween. Consequently, because the director rotates within the substrate surface in this display system, the problem that a relationship between the light transmission quantity and the voltage application quantity in the case of TN system, when watching in the direction of the director and in the direction of normal of the substrate has a large difference, does not occur, then it is possible to obtain good picture while watching from very wide angle of vision.
However, in the conventional IPS system of liquid crystal display apparatus, there is a problem that the pixel electrodes and the common electrodes are formed in the straight-line shape mutually, and the liquid crystal molecules perform one directional rotation, in this case of watching from an oblique direction in white indication condition, colored condition occurs. Accordingly, a multi domain structure is proposed for solving the problem, which forms the pixel electrodes and the common electrodes in such a way as to bend the pixel electrodes and the common electrodes at bending point more than one to form a plurality of domains in which orientation direction thereof is different within one pixel.
As to the aforementioned conventional technique, it is explained with referring to FIG. 1A, FIG. 1B and FIG. 2. FIG. 1 is a view illustrating a structure of a conventional IPS system liquid crystal display apparatus. FIG. 1A is a plan view and FIG. 1B is a sectional view along Exe2x80x94E line of FIG. 1A. Further, FIG. 2 is a view schematically illustrating electric field between electrodes and rotational direction of the liquid crystal molecules. This liquid crystal display apparatus is constituted by a first transparent substrate 1 on which TFT is formed, a second transparent substrate 2 on which a color filter (CF) is formed, and liquid crystal 17 that is sandwiched therebetween, and in the first transparent substrate 1 forms a gate line 2 and a signal line 6 at approximately right angle, and TFT 5 is arranged in the shape of matrix at an intersection thereof. Furthermore, the pixel electrode 7 and the common electrode 3 are alternately formed in parallel with each other at the respective pixels, bending at the bent point more than one. Moreover, a black matrix 12 for shading extra light, color layer 13 for performing color indication of three RGB colors and flattening film 14 for covering them are formed on the second transparent substrate 11.
Then, orientation film 18 is coated to opposite surfaces of these first transparent substrate 1 and second transparent substrate 11, and the liquid crystal 17, homogeneously oriented in approximately parallel with extended direction of the signal line 6, is sandwiched between both substrates 1, 11. A polarization plate 16a is affixed to outside of the substrate 1. A conductive film 15 is formed at outside of the substrate 11, and a polarization plate 16b is affixed to outside of the conductive film 15. A polarization axis of both polarization plate 16a, 16b are at right angles with each other, one polarization axis is set in parallel with oriented direction of the liquid crystal molecule 17a. Then, write of electric potential is made to execute to the pixel electrode 7 through the TFT 5 to give lateral electric field to the bent pixel electrodes 7 and the bent common electrodes 3 therebetween, thus indication is made to control so that operation allows the liquid crystal 17 to be subjected to twist deformation within a surface parallel to the substrates 1, 11.
According to this method, when the voltage is applied to the pixel electrodes 7 and the common electrodes 3 therebetween, as illustrated in FIG. 2, the electric field 25 is generated in each different direction at two regions (upper region and lower region of FIG. 2) that are divided by the line which links top of the bent sections, therefore, the liquid crystal 17a which is initially oriented in the upper direction and the lower direction of FIG. 2 is twisted in two directions. Then, when watching from an oblique direction in the white indication condition, since the liquid crystal molecules 17a of the two regions compensate with each other, effect is obtained that colored condition is reduced. Furthermore, an equipotential surface 24 is formed in parallel with both the pixel electrodes 7 and the common electrodes 3.
However, in the conventional multi-domain liquid crystal display apparatus, since the initially oriented direction of molecules 17a is approximately right angle to the electric field direction in a adjacent area close to the line which joins tops of bent sections of the pixel electrode 7 or common electrode 3, rotational direction of the liquid crystal molecules 17a depends on whether the liquid crystal molecules 17a rotate in which direction depends on shape of the bent section, and when shapes of the bent sections are fluctuated depending on manufacturing errors, irregularities occur in connection with its orientation direction of the liquid crystal molecules 17a, resulting in, thus, the problem that disclination occurs. Furthermore, since the liquid crystal molecules 17a of the domain of both sides of the bent section rotate in the opposite direction mutually, motion of the liquid crystal molecules 17a close to the line joining top of the bent section is inhibited by the liquid crystal molecules 17a of the both sides, as a result, there is the problem that delay of response occurs.
Explained the circumstances referring to FIG. 2, the liquid crystal molecules 17a placed at upper section of FIG. 2 rotates clockwise because left-down electric field 25 acts to upper and lower initial orientation direction of this liquid crystal molecules 17a, on the other hand, the liquid crystal molecules 17a placed at lower section of FIG. 2 rotate counterclockwise because left-up electric field 25 acts to the liquid crystal molecules 17a, however, the liquid crystal molecules 17a existing in the region 23 of unstable orientation direction close to the line which joins tops of bent sections rotate in the direction without intention in response to the shape of the bent section sensitively, as a result, rotating in unexpected direction depending on slight shape irregularity or deviation of the initial orientation direction.
Further, generally, respective liquid crystal molecules 17a of the liquid crystal 17, under the ON or OFF condition of the voltages, do not independently rotate mutually but each liquid crystal molecule 17a exerts an influence mutually on the basis of elastic property, in which one liquid crystal molecule 17a rotates, then the other liquid crystal molecule 17a is coupled to this rotation, thus group of the liquid crystal molecules 17a perform twist deformation simultaneously. Namely, on the occasion of ON or OFF of the voltage, the liquid crystal 17 deforms in such a way that elastic power depending on elastic constants K11, K22, and K33 corresponding to each distortion of spread, twist, and bend respectively acts on the liquid crystal 17.
Considered actions of the liquid crystal molecule 17a having such elastic property in the area close to the bent point of FIG. 2, in the white indication condition where the voltage is applied to the common electrodes 3 and the pixel electrodes 7 therebetween, the liquid crystal molecule 17a at upper position of a center line is intended to rotate in the opposite direction against the liquid crystal molecule 17a at lower position of the center line, thereby, movement of the liquid crystal molecules 17a close to the line joining tops of the bent sections are influenced by the elastic force of the aforementioned upper and lower positioned liquid crystal molecules 17a is interrupted and response thereof slows down.
It is an object of the present invention to provide a liquid crystal display apparatus, which can achieve to prevent disclination, and to allow response to be speeded up and to cause luminance to be enhanced with high aperture rate.
A first aspect of a liquid crystal display apparatus according to the present invention comprises a pair of substrates opposing to each other and a liquid crystal sandwiched between the pair of substrates. In one side of the pair of substrates, a plurality of gate lines and a plurality of signal lines are provided to cross each other, which are at approximately right angles to each other. TFT is provided close to an intersection of the gate line and the signal line. Pixel electrodes and common electrodes are provided at each pixel surrounded by the gate line and the signal line. Each of which has bent points more than one and is alternately formed in parallel to mutually The IPS system liquid display apparatus causes liquid crystal molecule to be rotated within a surface in approximately parallel with the substrate by applying voltage applied to the pixel electrode and the common electrode therebetween. Both the pixel electrode and the common electrode comprise bent sections, and projected sections projecting toward concave section of the bent section of an opposite electrode side from convex side top section of the bent section. Also, the common electrode around the pixel disposed close to the signal line is formed in a shape of straight line along the signal line in connection with its outer edge at the side of the signal line.
In the present invention, the liquid crystal display apparatus can adopt a configuration wherein when viewed from the normal of the substrate, the projected section and the concave section of the bent section of the opposite electrode are formed so that both are not overlapped with each other.
Also, in the present invention, the liquid crystal display apparatus can adopts a configuration wherein the projected section is formed in rectangular shape, in rectangular shaped projected body provided with a pointed end section projecting toward the concave section of the bent section of the opposite electrode, in rectangular shaped projected body provided with a circular arc shaped pointed end section, or in V-character shape projecting toward the concave section of the bent section of the opposite electrode.
Further, in the present invention, the liquid crystal display apparatus preferably adopts a configuration wherein the number of bent point of the pixel electrode and the common electrode is taken to be n (n is odd numbers more than 1), adjacent the pixel electrode and the common electrode are formed, and unit pixel which becomes aperture section is enclosed by light shading section, in cases where length of electrode extending direction of the unit pixel is taken to be a, length of electrode opposite direction of the unit pixel is taken to be b, width of the projected section is taken to be d, and a ratio of length of the projected section to clearance between the pixel electrode and the common electrode is taken to be xcex7, in which combination among n, d, and xcex7 is preferably selected so that following equation that indicates an aperture rate becomes maximum:
(axe2x88x92ndxcex7)xc3x97(bxe2x88x92(axc3x97tan xcex8)/(n+1))/ab 
Furthermore, in the present invention, the liquid crystal display apparatus preferably adopts a configuration wherein width of the signal line is taken to be D, distances between outer edge of the common electrode around the pixel disposed at a position adjacent to the signal line and the signal line is taken to be E, and width of part of the narrowest width of the common electrode is taken to be F, in which F is preferably set so that F becomes larger value than Dxc3x970.75xe2x88x92E.
Also, in the present invention, the liquid crystal display apparatus preferably adopts a configuration wherein film thickness of a passivation film is set so that a difference in level on the passivation film, which is formed at upper layer of the pixel electrode and the common electrode becomes less than 200 nm. Further, in the present invention, the liquid crystal display apparatus preferably adopts a configuration wherein the TFT is disposed in such a way that gate length direction of the TFT is in approximately parallel to or at approximately right angles to initial orientation direction of a liquid crystal molecule. Furthermore, in the present invention, the liquid crystal display apparatus adopts a configuration wherein the TFT is disposed close to an intersection of the gate line and the signal line at wide width side of the common electrode existing at side end section of the gate line among the common electrodes disposed close to the signal line.
In a second aspect of the liquid crystal display apparatus according to the present invention, the liquid crystal molecule is initially oriented obliquely to a direction which is at right angles to the gate line, and the TFT is stationed so that a gate length direction of the TFT is in approximately parallel to the initial orientation direction or is at approximately right angles to the orientation direction.
In a third aspect of a liquid crystal display apparatus according to the present invention, the common electrode around the pixel arranged close to the signal line is formed in such a way that outer edge of the common electrode at the signal line side is formed in the straight line shape along the signal line, and the TFT is stationed close to an intersection between the gate line and the signal line, which intersection exists at the wide width side of the common electrode in the gate line side end section among the common electrodes arranged close to the signal line.